Consolidated Statements of Cash Flows - USD ($) $ in Thousands	6 Months Ended
	Jun. 30, 2015	Jun. 30, 2014
Document Fiscal Year Focus	2015
Cash flows from investing activities:
Proceeds from Deposits on Real Estate Sales	$ 4,500
Cash flows from financing activities:
Net proceeds from common stock issuance	1,173
Parent Company [Member]
Proceeds from Issuance of Unsecured Debt	0	$ 248,705
Cash flows from operating activities:
Net income	69,271	56,217
Adjustments to reconcile net income to net cash provided by operating activities:
Depreciation and amortization	72,218	73,928
Amortization of deferred loan cost and debt premium	5,058	5,675
Amortization and (accretion) of above and below market lease intangibles, net	(936)	(1,698)
Stock-based compensation, net of capitalization	5,620	4,534
Equity in income of investments in real estate partnerships	(12,324)	(16,640)
Gain on sale of real estate	(6,460)	(2,406)
Provision for impairment	0	(225)
Early extinguishment of debt	61	0
Distribution of earnings from operations of investments in real estate partnerships	(22,719)	(18,736)
Loss on settlement of derivative instruments	0	(4,648)
Gain on derivative instruments	0	(9)
Deferred compensation expense	581	830
Realized and unrealized gain on investments	(1,000)	(847)
Changes in assets and liabilities:
Restricted cash	1,587	37
Accounts receivable	(5,895)	(10,365)
Straight-line rent receivables, net	(3,552)	(3,062)
Deferred leasing costs	(5,470)	(5,323)
Other assets	(3,209)	(2,016)
Accounts payable and other liabilities	(12,004)	(1,964)
Tenants’ security and escrow deposits and prepaid rent	1,270	(904)
Net cash provided by operating activities	127,413	119,596
Cash flows from investing activities:
Acquisition of operating real estate	0	(79,444)
Proceeds from Deposits on Real Estate Sales	(4,500)	0
Real estate development and capital improvements	(109,118)	(93,764)
Proceeds from sale of real estate investments	26,567	7,790
Investments in real estate partnerships	(1,344)	(4,287)
Distributions received from investments in real estate partnerships	15,014	21,496
Dividends on investments	87	66
Acquisition of securities	(20,581)	(18,195)
Proceeds from sale of securities	17,169	3,702
Net cash used in investing activities	(76,706)	(162,636)
Cash flows from financing activities:
Net proceeds from common stock issuance	955	0
Redemption of preferred stock and partnership units	0	(300)
Distributions to limited partners in consolidated partnerships, net	(1,722)	(938)
Distributions to exchangeable operating partnership unit holders	(151)	(152)
Dividends paid to common stockholders	(90,625)	(85,928)
Dividends paid to preferred stockholders	(10,531)	(10,531)
Proceeds from unsecured credit facilities	85,000	245,000
Repayment of unsecured credit facilities	(40,000)	(235,000)
Proceeds from notes payable	2,399	655
Repayments of Notes Payable	76,027	6,615
Scheduled principal payments	(2,921)	(3,413)
Payment of loan costs	(3,746)	(2,391)
Net cash used in financing activities	(137,369)	(908)
Repayments of Unsecured Debt	0	150,000
Net decrease in cash and cash equivalents	(86,662)	(43,948)
Cash and cash equivalents at beginning of the period	113,776	80,684
Cash and cash equivalents at end of the period	27,114	36,736
Supplemental disclosure of cash flow information:
Cash paid for interest (net of capitalized interest of $4,015 and $3,272 in 2015 and 2014, respectively)	53,458	54,083
Income Taxes Paid	697	0
Supplemental disclosure of non-cash transactions:
Mortgage loans assumed for the acquisition of real estate	0	78,049
Change in fair value of derivative instruments	4,494	24,953
Common stock issued for dividend reinvestment plan	683	604
Stock-based compensation capitalized	1,493	1,410
Contributions from limited partners in consolidated partnerships, net	13	95
Non-controlling interest recorded, fair value	0	15,385
Common stock issued for dividend reinvestment in trust	432	384
Contribution of stock awards into trust	1,475	1,847
Distribution of stock held in trust	1,898	4
Available-for-sale Securities, Gross Unrealized Gain (Loss)	(30)	914
Partnership Interest [Member]
Proceeds from Issuance of Unsecured Debt	0	248,705
Cash flows from operating activities:
Net income	69,271	56,217
Adjustments to reconcile net income to net cash provided by operating activities:
Depreciation and amortization	72,218	73,928
Amortization of deferred loan cost and debt premium	5,058	5,675
Amortization and (accretion) of above and below market lease intangibles, net	(936)	(1,698)
Stock-based compensation, net of capitalization	5,620	4,534
Equity in income of investments in real estate partnerships	(12,324)	(16,640)
Gain on sale of real estate	(6,460)	(2,406)
Provision for impairment	0	(225)
Early extinguishment of debt	61	0
Distribution of earnings from operations of investments in real estate partnerships	(22,719)	(18,736)
Loss on settlement of derivative instruments	0	(4,648)
Gain on derivative instruments	0	(9)
Deferred compensation expense	581	830
Realized and unrealized gain on investments	(1,000)	(847)
Changes in assets and liabilities:
Restricted cash	1,587	37
Accounts receivable	(5,895)	(10,365)
Straight-line rent receivables, net	(3,552)	(3,062)
Deferred leasing costs	(5,470)	(5,323)
Other assets	(3,209)	(2,016)
Accounts payable and other liabilities	(12,004)	(1,964)
Tenants’ security and escrow deposits and prepaid rent	1,270	(904)
Net cash provided by operating activities	127,413	119,596
Cash flows from investing activities:
Acquisition of operating real estate	0	(79,444)
Proceeds from Deposits on Real Estate Sales	(4,500)	0
Real estate development and capital improvements	(109,118)	(93,764)
Proceeds from sale of real estate investments	26,567	7,790
Investments in real estate partnerships	(1,344)	(4,287)
Distributions received from investments in real estate partnerships	15,014	21,496
Dividends on investments	87	66
Acquisition of securities	(20,581)	(18,195)
Proceeds from sale of securities	17,169	3,702
Net cash used in investing activities	(76,706)	(162,636)
Cash flows from financing activities:
Net proceeds from common units issued as a result of common stock issued by Parent Company	955	0
Redemption of preferred stock and partnership units	0	(300)
Distributions to limited partners in consolidated partnerships, net	(1,722)	(938)
Dividends paid to common stockholders	(90,776)	(86,080)
Dividends paid to preferred stockholders	(10,531)	(10,531)
Proceeds from unsecured credit facilities	85,000	245,000
Repayment of unsecured credit facilities	(40,000)	(235,000)
Proceeds from notes payable	2,399	655
Repayments of Notes Payable	76,027	6,615
Scheduled principal payments	(2,921)	(3,413)
Payment of loan costs	(3,746)	(2,391)
Net cash used in financing activities	(137,369)	(908)
Repayments of Unsecured Debt	0	150,000
Net decrease in cash and cash equivalents	(86,662)	(43,948)
Cash and cash equivalents at beginning of the period	113,776	80,684
Cash and cash equivalents at end of the period	27,114	36,736
Supplemental disclosure of cash flow information:
Cash paid for interest (net of capitalized interest of $4,015 and $3,272 in 2015 and 2014, respectively)	53,458	54,083
Income Taxes Paid	697	0
Supplemental disclosure of non-cash transactions:
Mortgage loans assumed for the acquisition of real estate	0	78,049
Change in fair value of derivative instruments	4,494	24,953
Common stock issued for dividend reinvestment plan	683	604
Stock-based compensation capitalized	1,493	1,410
Contributions from limited partners in consolidated partnerships, net	13	95
Non-controlling interest recorded, fair value	0	15,385
Common stock issued for dividend reinvestment in trust	432	384
Contribution of stock awards into trust	1,475	1,847
Distribution of stock held in trust	1,898	4
Available-for-sale Securities, Gross Unrealized Gain (Loss)	$ (30)	$ 914